1. Field of the Invention
The present invention relates to a method for continuous rolling by continuously welding the rolled materials at an intermediate stage of a rolling line after applying several passes of rolling of billets, and relates to an apparatus therefor.
2. Description of the Related Art
A known continuous rolling method to produce wire, rod, or to shape steel with energy-saving and high efficiency comprises the steps of discharging billets from a heating furnace one at a time, welding the rear end of a preceding billet with the front end of a succeeding billet by a single unit of travelling flash-butt welder, removing the burr from the welded portions using a scarfer or the like, heating the thus formed continuous billet to a temperature necessary for rolling in an induction heating furnace, then continuously rolling the continuous billet in a rolling mill group: (disclosed in, for example, unexamined Japanese patent publication No.52-43754(1977)). Alternatively, there is a continuous rolling method in which billets discharged from a heating furnace are joined together by welding to form a continuous billet, and the continuous billet is heated again in the heating furnace, wherein also a single unit of travelling flash-butt welder is used: (disclosed in, for example, examined Japanese patent publication No.52-11722(1982)).
Shortening the cycle time for treating a single billet is an important issue in the continuous rolling of billets. In this respect, the weight of an ordinary billet is in a range of from 0.5 to 2 ton, and the necessary cycle time to treat a single billet is less than 1 min. to assure a production capacity of 70 to 80 ton/hr or more. Since conventional continuous rolling processes use only one on-line travelling flash-butt welder, as described above, the welding time inherent to the travelling flash-butt welder is difficult to shorten. Consequently, it is impossible to realize a cycle time of less than 1 min. in the prior art.
A possible method to shorten the cycle time is to incorporate two travelling welder units to realize a shorter cycle time operation. However, a system of two travelling welders increases investment cost and requires large capacity power source. Another possible method is to reduce the cross sectional area of the billet through rolling in a specific number of rolling mill groups, to provide the intermediate rolled materials in a free state, to adjust the position of the intermediate rolled materials, and to perform the weld-joining to reduce the welding time. These methods, however, have a disadvantage that, when the intermediate rolled materials become long, the methods cannot be adopted owing to the limitation of interstand distance.